We proposed a new method for quantifying the micro/nano-scale wear volume (i.e., volume of wear loss) in a test to characterize the wear-resistance of nanocomposites. Effects of wear load and pass (a pattern of scan cycles), and nanoparticle content on the wear behavior of silica nanoparticle-reinforced composites (EP/SiO2) were studied accordingly. The multiple nano-scratch patterning technique was carried out for the wear test. Images of sample surface, before/after the test, obtained using in-situ scanning probe microscopy (SPM) were used to calculate the wear volume. Our results indicate that the wear mechanism transits from a plastic-deformation dominated mode to a fatigue-wear dominated mode when the wear load and pass increase above a threshold. The transition threshold increases with the nanoparticle content, and the increase corresponds to an improvement in wear resistance of nanocomposites. This transition threshold can be a different way, rather than using the conventional mechanical properties (e.g., surface hardness and stiffness), to characterize the wear resistance of materials such that the wear condition is taken into account.